High-Performance Insulation in Thinner Assemblies

Incorporating insulation into walls, floors, roofs, and other areas of a building enclosure is required by code and needed in order to control heat loss or gain in a buildings. The design challenge has often been balancing the need to meet R-value targets for the insulation with the thickness of the construction assembly (i.e., walls, roofs, etc.) required to incorporate that level of insulation. The default approach for many is to use some type of fibrous insulation in batt, blanket, or loose form installed between wood or metal framing members. Since such insulation is generally available with R-values in the range of R-3 to R-4 per inch, framing depth has increased in many projects to accommodate the need for more inches of insulation to meet the targeted total R-value. For places where still more insulation is needed, then continuous insulation is added outside of the framing or in some other manner (as in continuous roof insulation over a roof deck) that is similarly built up by the inch to achieve the needed total R-value. Of course, part of the struggle is the recognition that increasing thicknesses also increase construction costs, not just of the construction assembly itself but also the details of things that integrate with them, such as windows, doors, skylights, etc. This issue is particularly exaggerated on existing buildings that are being renovated.

Hearing the outcry from designers and contractors for ways to achieve higher thermal values in less thickness, product manufacturers offer a number of options. There are various types of insulation on the market, but it is important to note that they have different circumstances where they are best fit to be used. In that light, we look at three types of advanced products in the following sections.

Photo courtesy of Kingspan Insulation LLC

XPS insulation is a commonly used rigid foam insulation board with very good insulation and moisture-resistant properties.

Extruded Polystyrene Insulation

There are a number of different types of rigid foam insulation made from different types of plastic foam and with different facings on them, or no facing as the case may be. One that has been in common use for some time is extruded polystyrene insulation board, commonly abbreviated as XPS. It is made by extruding thermoplastic polystyrene foam through a machine to form it into continuous boards that are cut to length (just like some metals are extruded for other purposes). This produces a comparatively dense insulation product with closed cells compared to the somewhat lighter expanded polystyrene (EPS), which can have an open-cell structure. Because of this makeup and the extrusion process, XPS offers superior cold-temperature performance when compared to many other insulation types. Specifically, it typically provides R-values on the order of R-5 per inch, meaning that it can achieve higher overall total R-values in less assembly thickness than fiber-based batts, blankets, or loose-fill.

XPS insulation also offers superior moisture resistance compared to fibrous insulation, meaning that it does not absorb water nor lose its R-value rating when wet. Because of this, it is often considered to be a superior choice for masonry cavity walls, below-grade walls and floors, and in inverted roofing applications. These are all moisture-prevalent applications, and XPS is often chosen to be specified in these circumstances. There are other rigid foam insulations, such as polyisocyanurate insulation, that may claim a higher R-value per inch, but those are not as well-suited for situations where moisture is a concern. Many designers find XPS to be a reliable and reasonably economical insulation solution when the total costs of different assemblies are compared.

Phenolic Insulation

In some cases, even higher R-values per inch are needed for code compliance or performance specifications. An alternative is rigid thermoset phenolic insulation, which is produced by mixing high-performance solids and phenolic resin with a surface acting agent. It is manufactured by a process in which a plastic foam forms an insulating core between two facers with a fiber-free closed-cell content. European formulations of phenolic insulation have been in use for several decades in both residential and commercial construction.

Phenolic insulation offers an extensive range of premium-performance insulation products for wall, floor, soffit/structural ceiling, rainscreen, and concrete sandwich wall-system applications. With an R-value of up to 17 per 2 inches of insulation (i.e., approximately 8.5 per inch), it is the thinnest among commonly used insulation products on the market. In addition to its superior insulation properties, phenolic insulation is based on a fiber-free, rigid, thermoset phenolic insulation core that resists moisture as well as water-vapor ingress. It also exhibits excellent fire performance with very low flame spread and smoke developed ratings when tested in accordance with ASTM E84/UL 723: Standard Test Method for Surface Burning Characteristics of Building Materials.

In terms of environmental impact, phenolic insulation boards are available that are manufactured with a blowing agent that has zero ozone depletion potential (ODP) and low global warming potential (GWP). By resisting moisture and water-vapor ingress, it also eliminates problems that can be associated with open-cell materials that absorb water and can result in reduced thermal performance. Similarly, phenolic insulation thermal properties are unaffected by air infiltration. The products are safe and easy to install, with no fibers that can irritate human airways and harm health.

The high R-values of phenolic insulation can help to reduce the build-out depth of residential and commercial wall systems, potentially leading to added rentable or sellable space on the interior. It is designed to offer a thin solution for common exterior wall continuous insulation applications. It will also help to reduce the length of fasteners and bracketry in commercial wall assemblies. This product has many applications for cavity wall, rainscreen, and soffit applications. When installed correctly, phenolic insulation is known for providing reliable long-term thermal performance over the lifetime of a building.

Images courtesy of Kingspan Insulation LLC

Phenolic insulation provides greater R-values per inch with very good fire performance and low environmental impact, making it a strong solution for exterior wall assemblies, among other locations.

Vacuum Insulated Panels

A new and very innovative insulation product is known as vacuum insulated panels (often called a VIP). This is a next-generation insulation comprising rigid panels with a microporous core, which is evacuated, encased, and sealed to form a thin, gas-tight envelope. It provides outstanding R-values by virtue of the literal vacuum formed in the panel all in an ultra-thin insulation solution. This product is designated as being applicable specifically to commercial roofing applications, offering thermal resistance values up to five times greater than XPS. For example, a 1.6-inch VIP product has an amazingly high R-value of R-46. Clearly, this is a solution for those times when space is tight and reduced thickness is critical to success.

As a means to substantiate these performance claims, manufacturers use ASTM C1667: Standard Test Method for Using Heat Flow Meter Apparatus to Measure the Center-of-Panel Thermal Transmission Properties of Vacuum Insulation Panels, which is the only test method designated by ASTM to be used specifically for testing center panel thermal resistance of VIPs. ASTM C1667 further states that VIPs fall outside the scope of the more commonly known test method ASTM C518: Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus. All vacuum insulated panels should be tested according to these protocols, and results of those tests should be made available from the manufacturers as part of the normal project submittal process to confirm the tested R-value results. Note that testing is based on the center of the panels. For edge conditions, calculations can be performed per the ASTM protocols to determine results.

These high R-values allow the roof insulation buildup height to be drastically reduced. For renovations or reroofing projects with height-restricted situations, such as parapet height and door threshold limitations, VIP insulation allows designers to meet code while eliminating the need for architectural renovations to accommodate the roof insulation system. It is worth noting that the products are also more than 90 percent recyclable by weight.

Manufacturers of insulation often offer multiple products. Therefore, many offer thermal calculation support for many products, and with some roofing insulation, they also offer a design service and installation support. This helps the architect be quite up to date on the innovative insulation board technologies that offer a higher R-value in minimal thicknesses, allowing for thinner wall system profiles. Andrew Wilson, commercial manager for Kooltherm & OPTIM-R with Kingspan Insulation LLC, sums it up this way: “High-performing insulation can help cut energy bills and makes for a very efficient building. Using a high-performance insulation product will allow for a building to go well above the energy code, and for someone who owns a building, the payback will be great over the life of the building.”

Image courtesy of Kingspan Insulation LLC

Vacuum insulation panels (VIPs) are an innovative product with superior R-values, which make them very suitable for roofing projects and renovation work.